For example, in a so-called short-pitch-type rubber track for construction machines in which plural cores are arranged at short pitches, when lugs are arranged on the outer peripheral surface of the rubber track in consideration of cut resistance or vibration reducing property, an end portion of one core among two cores adjacent to each other in the circumferential direction is likely to become a portion not covered with the lug. As a result, at a portion of the end portion of the core not covered with the lug, a covering thickness of the core covered with the rubber elastic body is thinner, which leads to a large stepwise difference in rigidity between a portion with the core and a portion without the core. Therefore, there existed a problem that, when the rubber track travels, strain is concentrated between these portions, and cracks called an edge-cutting are likely to occur at the portion corresponding to the end portion of the core of the rubber elastic body.
To solve such a problem as this, Patent Literature 1 proposes that a ridge 54 extending between lugs 53 located before and after the ridge 54 be formed on the outer peripheral surface of a rubber elastic body 52 and at portions corresponding to right and left end portions of a core 51, as exemplarily shown in FIG. 5, which relates to a developed plan view and a sectional view in the width direction on the outer peripheral surface side of the half width of a rubber track. With this technique, since the ridge 54 is formed on the outer peripheral surface of the rubber elastic body 52 and at the portions corresponding to the right and left ends of the core 51 where the edge-cuttings are most likely to occur, the strain occurring at the right and left ends of the core is made dispersed, and the occurrence of cracks at the rubber elastic body 52 can be prevented.
However, as can be clearly understood from the sectional view exemplarily shown in FIG. 5(b), with the proposed technique, an inclined angle θ of an inclined plane 54a of the ridge 54 whose thickness gradually decreases toward the side edge side of the rubber elastic body 52, with respect to a vertical plane is significantly large as compared with a similar inclined angle θ1 of an inclined face 53a of each of the lugs 53 on the side edge side of the rubber elastic body. Therefore, even at the portion where the ridge 54 is formed, the thickness of the rubber covering the end portion of the core 51 is significantly small as compared with that at the lug 53, and hence, the crack directly occurring at a portion of the rubber elastic body 52 corresponding to the end edge of the core 51 still cannot be sufficiently prevented when the side edge of the rubber track is rubbed with a curbstone or the like. Further, because of the difference between the inclined angles θ, θ1 described above, a spur 55 formed by an angled portion adjacent to the inclined face 53a of the lug 53 is made outstanding throughout the entire length thereof. The spur 55 is likely to be caught by the curbstone or the like, which causes the strain to be concentrated on the portion corresponding to the end edge of the core. This further promotes the occurrence of cracks at the rubber elastic body 52 as described above.
Further, for the similar purpose of preventing the occurrence of cracks, as described in Patent Literature 2, there is proposes a rubber track having cores arranged at predetermined pitches and covered with a rubber body portion, in which the wall thickness of the rubber body portion at an end portion in the width direction of the rubber track is substantially equal in all the directions of an inner peripheral side, outer side and outer peripheral side from the end portion of the core. According to this proposal, even when forces from any direction act on the end portion of the rubber track due to riding over obstacles, and the like, the wall thickness between the end portion of the rubber track and the end portion of the core of the rubber body portion is substantially equal, and hence, stress concentration is less likely to occur. As a result, there is no possibility of occurrence of the edge-cuttings and the like, whereby durability of the rubber track improves.
However, with the rubber track described in Patent Literature 2, there is a problem that a side portion of the track is brought into point-contact with a curbstone in a case where the side portion is formed into an outwardly-convex curved shape, and hence, cracks due to the stress concentration are more likely to occur at the side portion. Further, in a case where a side face of the track is formed into a flat face, the stress concentration is less likely to occur, but there arises a problem that it is difficult to secure the thickness of the rubber on the lug side sufficient to improve the crack resistance at the end of the core.